Ultrasonic diagnosing apparatus

ABSTRACT

An ultrasonic diagnostic apparatus transmits an ultrasonic beam into an object to be examined using a multi-ring arrangement formed with transducer elements arrayed two-dimensionally in concentric rings and receives an echo so as to create a tomogram or a three-dimensional image of the object. To correct for focusing error due to the difference in length of ultrasound propagating paths, the ultrasonic diagnostic apparatus groups the transducer elements so as to form a multi-ring arrangement, transmits/receives ultrasonic beams with a delay to each ring of the multi-ring arrangement and scans the ultrasonic beam so as to create an ultrasonic image, measures delay error due to presence of a sound speed non-uniformity portion of the object and changes either the coupling of the multi-ring or the delay time based on the measurement error.

FIELD OF THE INVENTION

The present invention relates to an ultrasonic diagnostic apparatus ofthe type used for acquiring an ultrasonic image of a diagnostic part byscanning the interior of an object to be examined in real time with anultrasonic beam formed with a two-dimensional transducer array; and,more particularly, the invention relates to an ultrasonic diagnosticapparatus which includes means for correcting a focusing error whichoccurs due to a difference in the length of propagating paths ofultrasound transmitted/received with a multi-ring type transducer inwhich a plural number of electronically transducers are bundled intoconcentric rings.

BACKGROUND OF THE INVENTION

An apparatus having a plural number of transducer composed of atwo-dimensional transducer array in which sector scanning is performedusing an ultrasonic beam (in an arbitrary direction) generated by atransmitting/receiving circular pattern of transducers formed in thetwo-dimensional transducer array is known. In this ultrasonic diagnosticapparatus, for example, if 64 64 transducers are disposed in thetwo-dimensional array, then the total number of transducers is 4,096.;and, ultrasonic scanning is performed with a separate delay controlprovided for each transducer element. In this case, a beam-formingcircuit with 4,096 channels is necessary. Realizing a beam-formingcircuit having such a large number of multi-channel delay circuits isdifficult. So, by thinning out the number of driven elements for formingone ultrasonic beam, the number of delay circuit channels in thebeam-forming circuit is reduced. But the S/N of signal acquired bythinning out the driven elements is deteriorated. So, the apparatus isrealized by comprising a beam-forming circuit having as many as delaychannels possible. For example, there is an apparatus that comprises abeam-forming circuit having a delay circuit of 256 channels fortransmitting and 256 channels for receiving.

As shown in FIG. 4, a linear scanning expanded field of view obtained bymoving the transmitting/receiving circular pattern of transducerelements 1, that are arrayed in a two-dimensional X, Y direction, and ascanning method in which a convex scanning is applied to two-dimensionsare proposed. In this case, the number of transducer elements 1 is morethan in said sector scanning type apparatus. So, for reducing the numberof channels in the beam-forming circuit, an apparatus is known thatproduces an ultrasound transmitting/receiving circular pattern 2 byelectronically bundling a plural number of transducer elements 1 in thetwo-dimensional array into a multi-ring arrangement with concentricrings, so as to give a consistent delay time to the transducer elementscomposing one ring of said multi-ring arrangement. The apparatustransmits/receives an ultrasonic beam with a delay time between rings,and forms an ultrasonic image by moving said circular pattern 2 in X, Ydirections.

As shown in FIG. 5, in said multi-ring arrangement, each ring is formedby the bundling of transducer elements in concentric rings of which thedistance L₁, L₂ . . . , from the single focal spot F is almost the same,and the diameter of the most exterior ring is diameter 2 for ultrasoundtransmitting/receiving. In this method, the bundling of transducerelements in concentric rings makes it possible to reduce greatly thenumber of channels in the beam forming circuit, which corresponds to thenumber of delay circuits, and the S/N of a signal acquired by using allelements in a circular pattern can be improved.

When considering the shape of an ultrasonic beam, a focusing calculationfor an ultrasonic beam in the object to be examined is traditionallyperformed under the condition that the speed of sound in an ultrasonicpropagation medium is uniform. As shown in FIG. 6, a traditionalapparatus comprises delay circuits 4, 4, . . . comprising one pertransducer element of the probe 3 having a plural number of transducersand an adder 5 for adding received signals output from these delaycircuits 4, 4, . . . Although reflected signals from focus point 6 inthe object propagate through medium 7 to reach each transducer element,the difference in the path length from the focus point to eachtransducer element causes a difference in the arrival time of eachreflected signal. In this case, the reflected signals reach thetransducer elements located in the center of probe 3 early, and, on theother hand, they reach the transducer elements at the ends late. So, theshape of the wave surface 8 in the received signals is not linear. Thus,the signals output from transducer elements in the center part of theprobe are delayed with a large amount of delay time in delay circuits 4corresponding to each received signal, and the signals output fromtransducer elements at the ends of the probe are delayed with a smallamount of delay time. The signals are then output to adder 5. With thesedelay operations, the wave surface 9 of the signal output from delaycircuits 4 is linear since the signals have the same phase. The receivedsignals having the same phase, such as shown by wave surface 9 in thiscondition, are added in adder 5 so as to form the combined signal 10.

But actually, as shown in FIG. 7, a sound speed non-uniformity part 11typically exists on the path from the focus point 6 in the object to theprobe 3, so that the wave surface of the received signal is disturbed,as shown at 8′. In this case, when performing the delay operation, whileassuming that the speed of sound is uniform, the wave surface of thereceived signals output from delay circuits 4 is distorted. as shown at9′, so that they do not have the same phase. Accordingly. the outputproduced in adder 5 does not increase in intensity as the signals areadded, so that its intensity is small, as shown by signal 10′.

On the Contrary, there is a technology referred to as an adaptiveultrasonic imaging method which operates to correct the delay amountproduced in said delay circuits 4 in accordance with the speed of soundin the medium. In the adaptive ultrasonic imaging technology, a mutualcorrelation method for correcting the delay amount by correctionprocessing of respectively received signals between adjacent channels,and a maximum value brightness method for searching for a brightnessmaximum while changing the delay amount of the delay circuits are known.

FIG. 8 is a block diagram which illustrates the mutual correlationmethod. In FIG. 8, a signal received from each transducer element, whichis not shown in the figure, is delayed by a predetermined amount by arespective delay circuit 4, 4, . . . This delay is possible by use ofanalog delay circuits or digital delay circuits. In this case, whenoutputs of adjacent channels in each transducer element, a mutualcorrelation processing is carried out with correlation device 12, andthe phase difference between the outputs of adjacent channels can beobtained. By detecting the phase difference value, transforming it tofocus data in correction processing part 13, and feeding the transformeddata back to focus controlling part 14, the delay amount produced by theindividual delay circuits 4.

FIG. 9 is a block diagram illustrating the maximum value brightnessmethod. In FIG. 9, a received signal from each transducer element, whichis not shown in the figure, is delayed in a respective delay circuit 4,4, . . . by a predetermined amount. The outputs delayed in therespective delay circuits 4, 4, . . . are added in adder 5., and thisoutput is input to maximum value detecting part 15. This maximum valuedetecting part 15 compares the input signal with the last input value,and, in case the input value is smaller than the last detected value,the focus data is slightly changed systematically in focus controllingpart 14. Then, after the phasing of the received echo signal has beenchanged by this focus data, the output of adder 5 is inputted to themaximum value detecting part 15, and judged again. After repeating thisoperation, when the detected value is formed to converge at the maximumvalue, its data is used as focus data.

However, as shown in FIG. 4 and FIG. 5, in an ultrasonic diagnosticapparatus in which a transmitting/receiving circular pattern 2 is formedby bundling transducer elements of a two-dimensional array intoconcentric rings to compose a multi-ring arrangement, in case there is asound speed non-uniformity part 11 on the path from focus point 6 to theprobe 3 in the object, since transducer elements 1 in thetwo-dimensional array are bundled in concentric rings as thus described,it is difficult to detect the phase difference due to said pathdifference for correcting for the influence of said sound speednon-uniformity part 11. Therefore, the phase difference of echo signalscaused by said path difference, due to the existence of the sound speednon-uniformity part 11, is not corrected. As a result, the image qualityis deteriorated because the ultrasonic beam becomes worse.

Thus, it is an object of the present invention to solve theabove-mentioned problems by providing an ultrasonic diagnostic apparatuswhich is able to correct a focusing error by detecting the phasedifference of echo signals which occur due to a difference in theultrasonic propagating path, even when its multi-ring arrangement oftransducers is composed by bundling transducers in a two-dimensionalarray for transducer elements in concentric rings.

SUMMARY OF THE INVENTION

To achieve the foregoing object, an ultrasonic diagnostic apparatus isprovided in accordance with the present invention, in which there is aprobe comprising a plural number of transducer elements formed as atwo-dimensional array for transmitting/receiving an ultrasound to anobject to be examined. A circular pattern of transducers for ultrasoundtransmitting/receiving is formed by bundling said two-dimensional arrayof transducer elements in concentric rings to form a multi-ringarrangement, and transmitting/receiving of an ultrasound is achievedwith the application of a delay between each ring in said multi-ringarrangement, so that an ultrasonic image is formed by scanning saidbeam. The ultrasonic diagnostic apparatus comprises means for measuringfocusing error that is produced due to a sound speed non-uniformity insaid object and for transmitting/receiving an ultrasonic beam that hasbeen corrected based on the measured error by changing at least one ofthe bundling of said multi-ring arrangement of transducers or the delaytime, and means for imaging the object by using an echo signal of thecorrected ultrasonic beam.

In the apparatus of the present invention, the circular pattern formedby said multi-ring arrangement, in which transducer elements in thetwo-dimensional array are bundled in concentric rings in said probe isdivided into a plural number of sections in a radial form from thecenter to the outside thereof. And, the focusing error due to a soundspeed non-uniformity in the object is measured between the ring sectorsof each divided section and between each section, and the ultrasonicbeam is corrected by feeding this measured value back to the delaycircuits.

Furthermore, in the apparatus of the present invention, a bundledarrangement of transducer elements form a circular pattern that isdifferent from that of said multi-ring arrangement composed by bundlingsaid transducer elements of a two dimensional array in said probe inconcentric rings. And, the focusing error due to a sound speednon-uniformity in the object between each sector is measured, and theultrasonic beam is corrected by feeding back this measured value to thedelay circuits and returning the form of the multi-ring to an initialsetting.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the overall arrangement of anembodiment of an ultrasonic diagnostic apparatus according to thepresent invention.

FIG. 2 is a diagram of a probe used in the first embodiment of thepresent invention.

FIG. 3 is a diagram of a probe used in the second embodiment of thepresent invention.

FIG. 4 is a diagrammatic plan view showing an example in which amulti-ring arrangement is set to probe in accordance with the presentinvention or in a traditional ultrasonic diagnostic apparatus, and inwhich transmitting and receiving of an ultrasonic beam andtwo-dimensional scanning are performed.

FIG. 5 is a diagram showing a principal of said multi-ring arrangement.

FIG. 6 is a diagram showing the formation of a traditional ultrasonicbeam.

FIG. 7 is a diagram showing the beam formation in a case where a soundspeed non-uniformity part is present in the medium when said ultrasonicbeam is formed.

FIG. 8 is a block diagram showing a circuit arrangement for correctingthe delay amount by using a mutual correlation method for producingadaptive image processing.

FIG. 9 is a block diagram showing a circuit arrangement for correctingthe delay amount by using a maximum value brightness method forproducing an adaptive image processing.

THE BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the present invention will be described indetail based on the accompanying drawings.

FIG. 1 is a block diagram showing an embodiment of an ultrasonicdiagnostic apparatus according to the present invention. This ultrasonicdiagnostic apparatus forms an ultrasonic beam with a two-dimensionaltransducer array and acquires an ultrasonic image of a diagnostic partin the interior of an object to be examined by scanning an ultrasonicbeam over the object in real time. As shown in FIG. 1, it comprises aprobe 20, an element selecting data part 21, a transmitting part 22,abeam-forming part 23, a transmitting/receiving separation circuit 24, asignal processing part 25, a scan converter 26, a monitor 27, and acontrolling part 28.

The probe 20 transmits an ultrasound to an object to be examined andreceives its echo. It is composed of a plural number of transducerelements 29, 29, . . . arrayed two-dimensionally. These transducerelement 29, 29, . . . are arrayed two-dimensionally such as 1˜m in the xdirection and 1˜n in the y direction in planar view, as shown in FIG. 4.And, the transducer elements 29, that are arrayed two-dimensionally, arealso bundled electronically to form a multi-ring arrangement in whichthere are concentric rings, and the multi-ring arrangement ahs the formof an ultrasonic transmitting/receiving circular pattern 30. A delaytime is given between each ring of said multi-ring arrangement totransmit and receive the ultrasonic beam. The ultrasonic beam scanningis performed by moving said circular pattern 30 at each cycle of thetransmitting/receiving of the ultrasound, whereby an ultrasonic image isformed. In addition, said multi-ring arrangement is made, for example,with fresnel-bundles.

In addition, connection switch groups 31 are connected for coupling anarbitrary delay channel in the beam-forming circuits to be described inlater to selected transducer elements. Furthermore, a switching controlpart 32 for controlling the switching operation is connected to theconnection switch groups 31.

Element selecting data part 21 memorizes element selecting data neededto form the transmitting/receiving circular pattern 30. In this regard,element selecting data read out from element selecting data part 21 istransferred to switching control part 32; and, by controlling saidswitching control part 32, the switching on and off of connection switchgroups 31 is controlled to form the transmitting/receiving circularpattern 30.

Transmitting part 22 supplies a transmitting signal for emitting anultrasound to the respective ultrasonic transducer elements with theapplication of a delay time such that the ultrasound transmitted fromeach transducer element which forms the transmitting/receiving circularpattern 30 of said probe 20 is focused at a desired focus point set inthe object. The beam-forming part 23 performs a desired focus process onrespective reflected echo signals received by the transducer elements 29of said probe 20 and forms a receiving beam by phasing and adding theseecho signals. The transmitting/receiving separation circuit 24 changesthe connection of said transmitting part 22 and beam-forming part 23 toselected transducer elements 29 to control whether an ultrasound istransmitted or received.

Signal processing part 25 inputs the signal output from saidbeam-forming part 23 and obtains the data of one scanning line bypredetermined processing, such as detecting, compression, filteringprocessing, edge emphasizing etc. The scan converter 26 inputs the dataoutput from said signal processing part 25 and forms image data fordisplay on the monitor 27, and it also performs scan conversion betweenultrasonic scanning and scanning for display and interpolationprocessing of image data or the like. Furthermore, monitor 27 displaysthe data received from said scan converter 26 as an ultrasonic image. Onthe display screen, a three-dimensional image or an arbitrary sliceimage is displayed. Controlling part 28 controls the operation of eachelement.

In accordance with the present invention, means is provided formeasuring a delay error in receiving a signal due to the presence of asound speed non-uniformity part in said object, and for correctingeither the bundling of transducer elements in the multi-ring arrangementor the delay time or both.

In a first embodiment, the circular pattern 30, composed of themulti-ring arrangements formed by electronically bundling thetwo-dimensional array transducer elements 29, 29, . . . of said probe 20in concentric rings, is divided into a plural number of regions inradial form from the center to the outside; and, between the diameter ofeach divided region, the delay error (focusing error) due to thepresence of a sound speed non-uniformity part (refer to 11 in FIG. 7) inthe object is measured to the correct beam.

A probe according to this first embodiment has transducer elementsarranged two-dimensionally. Although this is omitted in FIG. 2, actuallythey are arrayed with a matrix arrangement in the directions X and Y asshown in FIG. 4. The transducer elements are electronically bundled intoa ring shape to form a circular pattern of annular array (multi-ring).This circular pattern is moved in the X direction or Y directionaccording to a cycle of transmitting/receiving for performing a linearscanning or a convex scanning with an ultrasonic beam, or sectorscanning with the beam without moving the circular pattern. With suchlinear scanning, convex scanning, or sector scanning, with thistwo-dimensional probe, image data of a three-dimensional volume isacquired from the object. This image data is taken into scan converter26 and transformed to the image data which is displayed on the screen ofthe monitor 27 as an ultrasonic slice image or a three-dimensionalultrasonic image.

To provide a simple illustration, a basic circular pattern for acquiringone image is shown in FIG. 2. In FIG. 2, the circular pattern composedof a multi-ring arrangement is effected by bundling said two-dimensionalarray transducer elements electronically in concentric rings so that thecircular pattern is divided into a plural number of regions in radialform from the center to the outside. For example, element selecting datais transferred from element selecting data part 21 shown in FIG. 1 toswitching control part 32. With the controlling of said switchingcontrol part 32, the dividing lines L₁, L₂ crossing the center of saidmulti-ring arrangement are formed, and these dividing lines L₁, L₂divide the multi-ring arrangement into four sectors Sa, Sb, Sc, Sd.

Each of the divided sectors Sa˜Sd is respectively connected totransmitting part 22 and beam-forming part 23, as shown in FIG. 1. And,to the multi-rings separated in each sector, delay data calculated onthe condition that the speed of sound is uniform in medium 7 (refer toFIG. 6) is added. That is to say, in FIG. 2, transmitting part 22 andbeam-forming part 23 are connected respectively to ring sections a₁, a₂,a₃, a₄. b₁,.b₂, b₃, b₄, c₁, c₂, C₃, C₄, d₁, d₂, d₃, d₄ in each of thedivided sectors Sa˜Sd. Thus, delay control is performed individually forthe respective divided rays. Accordingly, the ultrasonic beam is focusedat some point with the prescribed delay.

At this time, if the speed of sound in medium 7 is consistent with thespeed of sound when the delay data is calculated, then the receivedsignal increases in amplitude with the same phase adding because thephase surface in the received signal after receiving phasing is the samephase as the case shown in FIG. 6. On the other hand, if a sound speednon-uniformity part 11 exists in medium 7, then the received signal willbe small because the phase surface in the received signal afterreceiving phasing is different, as shown in FIG. 7.

In accordance with the present invention, as shown in FIG. 2, themulti-ring arrangement is divided into, for example, four sectors Sa˜Sd,so that the phase error (this corresponds to focusing error) iscalculated with respect to the correlation of received signals afterreceiving phasing between the channel of transducer elements in eachdivided sector and is corrected in the same manner as shown in FIG. 8.That is to say, to each received signal after receiving phasing, thephase difference is calculated by mutual correlation between adjacentsectors in each ring divided in each sector Sa˜Sd, as shown in FIG. 2,and correlation processing is performed between each ring in eachsector.

For example, in FIG. 2, in the multi-ring arrangement divided into foursectors Sa˜Sd, mutual correlation processing is performed betweenadjacent sectors, such as a₁ and b₁, b₁ and c₁, c₁ and d₁, d₁ and a₁ inthe most interior ring. In addition, mutual correlation processing isperformed between adjacent sectors, such as a₂ and b₃, b₂ and c₂, c₂ andd₂, d₂ and a₂ in the second ring. Furthermore, in the third and thefourth rings as well, mutual correlation processing is performed betweenadjacent sectors. Also, to acquire a relationship between each ring ineach sector, the correlation processing between adjacent rings a₁ anda₂, a₂ and a₃, a₃ and a₄ in sector Sa is performed. In the sector Sb,the correlation processing is performed between adjacent rings b₁ andb₂, b₂ and b₃, b₃ and b₄. Furthermore, in sectors Sc, Sd as well,correlation processing is performed between adjacent rings. In thisregard, the method of correlation processing is not restricted to theabove-described sequence. Other methods can be used.

On the other hand, it is preferable to correct the phase error bycalculating the delay amount that brings about maximum intensity bychanging the delay amount of the beam-forming part between channels oftransducer elements in each divided sector in the same way as shown inFIG. 9, under the condition that, for example, a multi-ring arrangementis divided into four sectors Sa˜Sd, as shown in FIG. 2. That is, it ispreferable to correct the phase error by calculating the delay amountthat brings about a maximum intensity by changing the delay amountconsecutively to each ring, which is divided into each sector Sa˜Sd,a₁,.a₂, a₃, a₄, b₁, b₂, b₃, b₄, c₁, c₂, C₃, C₄, d₁, d₂, d₃, d₄.

Next, a second embodiment of the present invention will be described. Inthis second embodiment, it is preferable to form a bundled circularpattern which is different from the circular pattern formed by bundlingtransducer elements arrayed two-dimensionally in said probe 20 to form amulti-ring arrangement having concentric rings, and to measure delayerror due to the presence of a sound speed non-uniformity part in theobject between each circular pattern (refer to 11 in FIG. 7) and tocorrect the beam.

FIG. 3 is a diagram of a probe representing the second embodiment. Thisprobe has a two-dimensional array of transducer elements. Eachtransducer element is connected to a respective delay circuit, and anideal delay is given for some focus point to calculate delay error bycorrelating the outputs of the transducer elements. In the same way asshown in FIG. 5, when a multi-ring arrangement is bundled, if thebundled transducer elements forming one ring are formed, for example,such that the difference in the travel time (distance) of the ultrasoundto the focus point F is in the range of/10 (is wave-length of theultrasonic beam), then the delay error is corrected by adding saidcalculated delay error to the travel time.

For example, it is assumed that a specified transducer element 33 has adelay error in the multi-ring arrangement n1, n2, n3, n4 shown in FIG.3. Although transducer element 33 is bundled into ring n2 in the idealstate, when the delay error is added to it, a correction is performedsuch that it is bundled into ring n3, whereby the delay error iscorrected. And, after having calculated a correction value of delayerror, the transducer element 33 is bundled so as to return to the ringin the original ideal state. Thus, it is not the diameter for forming anultrasonic beam actually (bundled ring n1˜n4), but the delay error thatis detected with transducer element in another bundled ring. And, thecorrection is performed so as to form the bundled ring in considerationof the delay error.

In the case mentioned above, if a transmitter and a beam-forming circuitare connected to all of the two-dimensional array transducer elements,as shown in FIG. 3, then the circuit scale is large. Thus, for example,it is preferable to bundle adjacent transducer elements into rectangularblocks and connect the transmitter and the beam-forming circuits tobundled transducer elements as a unit. In addition, also in the secondembodiment, it is preferable to correct the phase error by calculatingthe delay amount in which the output signal is a maximum value bychanging the delay amount of the beam-forming part, as shown in FIG. 9.

As thus described, the present invention comprises means for measuringfocusing error which occurs due to the presence of a sound speednon-uniformity part in the object and for correcting one or both ofbundling or delay time of the multi-ring arrangement havingtwo-dimensional array transducer elements in concentric rings. Thus, theinterior of the object can be imaged with a corrected beam, so that theimage quality of the ultrasonic image is improved.

1. An ultrasonic diagnostic apparatus comprising a probe havingtwo-dimensional array of transducer elements for transmitting andreceiving ultrasonic waves to an object to be examined, in which acircular pattern of transducer elements is formed for transmitting andreceiving an ultrasound signal by bundling the transducer elements ofsaid two-dimensional array electronically to compose a multi-ringarrangement of transducer elements in concentric rings, and anultrasound beam is transmitted and received with application of a delaytime between each ring of said multi-ring arrangement, wherein saidultrasonic diagnostic apparatus further comprises means for transmittingand receiving an ultrasonic beam that has been corrected using saidmulti-ring arrangement by measuring a focusing error due to the presenceof a sound speed non-uniformity interior of said object and modifying atleast one of the manner of bundling of said multi-ring arrangement orthe delay time based on the measuring error, and means for imaging theobject with an echo signal formed of the corrected ultrasonic beam. 2.An ultrasonic diagnostic apparatus according to claim 1, wherein themulti-ring arrangement of transducer elements formed by bundlingtransducer elements of the two-dimensional array in said probe inconcentric rings is divided into a plural number of sections in a radialshape from the center to the outside of the circular pattern, and afocusing error due to the presence of a sound speed non-uniformity partin the object is measured between each section of the divided circularpattern or each section of the concentric rings, and the ultrasonic beamis corrected by feeding back a measured value to delay circuits in saidtransmitting and receiving means.
 3. An ultrasonic diagnostic apparatusaccording to claim 1, wherein a bundled arrangement of transducerelements is provided that is different from that of said multi-ringarrangement composed by bundling said transducer elements of saidtwo-dimensional array of said probe in concentric rings, and a focusingerror due to the presence of a sound speed non-uniformity part in theobject is measured between each circular pattern, and the ultrasonicbeam is corrected by feeding back a measured value to delay circuits insaid transmission and receiving means and returning the multi-ringarrangement to an initial setting.
 4. An ultrasonic diagnostic apparatuscomprising: a probe having a two-dimensional array of transducerelements; transducer selection means for electronically bundlingtransducer elements into a multi-ring arrangement composed of a pluralnumber of rings, means for dividing said multi-ring arrangement into aplural number of sections; means for calculating a focusing errorbetween sections in said multi-ring arrangement; means for feed-backcorrecting said calculated focusing error relative to a set delay timeto produce a corrected focusing error signal; a beam-forming partcomprised of delay circuits for applying a delay time to each ring ofsaid multi-ring arrangement of transducer elements in response to acorrected focusing error signal and an adder circuit for adding theoutputs of said each delay circuits; and means for imaging an outputsignal of said beam-forming part.
 5. An ultrasonic diagnostic apparatusaccording to claim 5, wherein means for calculating the focusing errorbetween sections in said multi-ring arrangement includes means forcalculating the focusing error between rings in one section.
 6. Anultrasonic diagnostic apparatus comprising: transducer selection meansfor initially forming a multi-ring arrangement of transducer elementscomposed of a plural number of rings from a two-dimensional array oftransducer elements; means for specifying transducer elements having afocusing error in each ring of said multi-ring arrangement; ringcorrection means for changing a specified transducer element to adifferent ring from initial ring location to correct the focusing error;a beam-forming part comprised of delay circuits for applying a delaytime to the transducer elements of each ring of said multi-ringarrangement and an adder circuit for adding the outputs of each of saiddelay circuits; and means for imaging an output signal of saidbeam-forming part.
 7. Ultrasonic diagnosing apparatus according to claim6, wherein means for specifying transducer elements having a focusingerror includes means for bundling a group of adjacent transducerelements different from a ring and assigning a transmitter andbeam-forming circuit to this bundled transducer group.
 8. An ultrasonicdiagnostic apparatus comprising: transducer selection means forinitially forming a multi-ring arrangement of transducer elementscomposed of a plural number of rings from a two-dimensional of arraytransducer elements; means for setting a multi-ring arrangement tocalculate a focusing error, separately from said formed multi-ringarrangement; a beam-forming part comprised of delay circuits forapplying a delay time to a respective ring of said multi ringarrangement of transducer elements initially formed or the multi-ringarrangement for calculating said focusing error, and an adder circuit